poly2.cpp

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    v3 = v;
    zero = 0;

    while(v3 != zero) {
        q = u3/v3;

        t1 = u1 - v1*q;
        t2 = u2 - v2*q;
        t3 = u3 - v3*q;

        u1 = v1;
        u2 = v2;
        u3 = v3;

        v1 = t1;
        v2 = t2;
        v3 = t3;
    }

	ptr=u3.start;
	t=(GF2m)1/ptr->an;
	u3.multerm(t,0);
	u1.multerm(t,0);
	u2.multerm(t,0);
	
    result[0] = u3;
    result[1] = u1;
    result[2] = u2;
}
 

Poly2 pow(const Poly2& f,int k)
{
    Poly2 u;
    int w,e,b;

    if (k==0)
    {
        u.addterm((GF2m)1,0);
        return u;
    }
    u=f;
    if (k==1) return u;

    e=k;
    b=0; while (k>1) {k>>=1; b++; }
    w=(1<<b);
    e-=w; w/=2;
    while (w>0)
    {
        u=(u*u);
        if (e>=w)
        {
           e-=w;
           u=(u*f);
        }
        w/=2; 
    }
    return u;
}

Poly2 pow(const Poly2& f,const Big& k,const Poly2& m)
{
    Poly2 u,t;
    Big w,e;
    if (k==0) 
    {
        u.addterm((GF2m)1,0);
        return u;
    }
    u=(f%m);
    if (k==1) return u;

    e=k;
    w=pow((Big)2,bits(e)-1);
    e-=w; w/=2;
    while (w>0)
    {
        u=(u*u)%m;
        if (e>=w)
        {
           e-=w;
           u=(u*f)%m;
        }
        w/=2; 
    }
    return u;
}

int degree(const Poly2& p)
{
    if (p.start==NULL) return 0;
    else return p.start->n;
}


BOOL iszero(const Poly2& p) 
{
    if (degree(p)==0 && p.coeff(0)==0) return TRUE;
    else return FALSE;
}

BOOL isone(const Poly2& p)
{
    if (degree(p)==0 && p.coeff(0)==1) return TRUE;
    else return FALSE;
}

void Poly2::clear()
{
    term2 *ptr;
    while (start!=NULL)
    {   
       ptr=start->next;
       delete start;
       start=ptr;
    }
    
}

Poly2& Poly2::operator=(int m)
{
    clear();
    if (m!=0) addterm((GF2m)m,0);
    return *this;
}

Poly2 &Poly2::operator=(const Poly2& p)
{
    term2 *ptr,*pos=NULL;
    clear();
    ptr=p.start;
    while (ptr!=NULL)
    {  
        pos=addterm(ptr->an,ptr->n,pos);
        ptr=ptr->next;
    }    
    return *this;
}

Poly2 operator+(const Poly2& a,const Poly2& b)
{
    Poly2 sum;
    sum=a;
    sum+=b;
    return sum;
}

Poly2 operator+(const Poly2& a,const GF2m& b)
{
    Poly2 sum=a;
    sum.addterm(b,0);
    return sum;
}

Poly2& Poly2::operator+=(const Poly2& p)
{
    term2 *ptr,*pos=NULL;
    ptr=p.start;
    while (ptr!=NULL)
    {  
        pos=addterm(ptr->an,ptr->n,pos);
        ptr=ptr->next;
    }    
    return *this;
}

Poly2& Poly2::operator*=(const GF2m& x)
{
    term2 *ptr=start;
    while (ptr!=NULL)
    {
        ptr->an*=x;
        ptr=ptr->next;
    }
    return *this;
}

BOOL operator==(const Poly2& a,const Poly2& b)
{
    Poly2 diff=a+b;
    if (iszero(diff)) return TRUE;
    return FALSE;
}

BOOL operator!=(const Poly2& a,const Poly2& b)
{
    Poly2 diff=a+b;
    if (iszero(diff)) return FALSE;
    return TRUE;
}

Poly2 operator*(const GF2m& z,const Poly2 &p)
{
    Poly2 r=p;
    r*=z;
    return r;
}

Poly2 operator*(const Poly2 &p,const GF2m& z)
{
    Poly2 r=p;
    r*=z;
    return r;
}

Poly2 operator/(const Poly2& a,const GF2m& b)
{
    Poly2 quo;
    quo=a;
    quo/=(GF2m)b;
    return quo;
}


Poly2& Poly2::operator/=(const GF2m& x)
{
    GF2m t=(GF2m)1/x;
    term2 *ptr=start;
    while (ptr!=NULL)
    {
        ptr->an*=t;
        ptr=ptr->next;
    }
    return *this;
}

void Poly2::multerm(const GF2m& a,int power)
{
    term2 *ptr=start;
    while (ptr!=NULL)
    {
        ptr->an*=a;
        ptr->n+=power;
        ptr=ptr->next;
    }
}

Poly2 invmodxn(const Poly2& a,int n)
{ // Newton's method to find 1/a mod x^n
    int i,k;
    Poly2 b;
    k=0; while ((1<<k)<n) k++;
    b.addterm((GF2m)1/a.coeff(0),0); // important that a0 != 0
    for (i=1;i<=k;i++)
         b=modxn (a*(b*b),1<<i);
    b=modxn(b,n);
    return b;
}

Poly2 modxn(const Poly2& a,int n)
{ // reduce polynomial mod x^n
    Poly2 b;
    term2* ptr=a.start;
    term2 *pos=NULL;
    while (ptr!=NULL && ptr->n>=n) ptr=ptr->next;
    while (ptr!=NULL)
    {
        pos=b.addterm(ptr->an,ptr->n,pos);
        ptr=ptr->next;
    }
    return b;
}

Poly2 divxn(const Poly2& a,int n)
{ // divide polynomial by x^n
    Poly2 b;
    term2 *ptr=a.start;
    term2 *pos=NULL;
    while (ptr!=NULL)
    {
        if (ptr->n>=n)
            pos=b.addterm(ptr->an,ptr->n-n,pos);
        else break;
        ptr=ptr->next;
    }
    return b;
}

Poly2 mulxn(const Poly2& a,int n)
{ // multiply polynomial by x^n
    Poly2 b;
    term2 *ptr=a.start;
    term2 *pos=NULL;
    while (ptr!=NULL)
    {
        pos=b.addterm(ptr->an,ptr->n+n,pos);
        ptr=ptr->next;
    }
    return b;
}

Poly2 reverse(const Poly2& a)
{
    term2 *ptr=a.start;
    int deg=degree(a);
    Poly2 b;
    while (ptr!=NULL)
    {
        b.addterm(ptr->an,deg-ptr->n);
        ptr=ptr->next;
    } 
    return b;
}

// add term to polynomial. The pointer pos remembers the last
// accessed element - this is faster. 
// Polynomial is stored with large powers first, down to low powers
// e.g. 9x^6 + x^4 + 3x^2 + 1

term2* Poly2::addterm(const GF2m& a,int power,term2 *pos)
{
    term2* newone;  
    term2* ptr;
    term2 *t,*iptr;
    ptr=start;
    iptr=NULL;
    if (a.iszero()) return pos;
// quick scan through to detect if term exists already
// and to find insertion point
    if (pos!=NULL) ptr=pos;      // start looking from here
    while (ptr!=NULL) 
    { 
        if (ptr->n==power)
        {
            ptr->an+=a;
            if (ptr->an.iszero()) 
            { // delete term
                if (ptr==start)
                { // delete first one
                    start=ptr->next;
                    delete ptr;
                    return start;
                }
                iptr=ptr;
                ptr=start;
                while (ptr->next!=iptr)ptr=ptr->next;
                ptr->next=iptr->next;
                delete iptr;
                return ptr;
            }
            return ptr;
        }
        if (ptr->n>power) iptr=ptr;
        else break;
        ptr=ptr->next;
    }
    newone=new term2;
    newone->next=NULL;
    newone->an=a;
    newone->n=power;
    pos=newone;
    if (start==NULL)
    {
        start=newone;
        return pos;
    }

// insert at the start

    if (iptr==NULL)
    { 
        t=start;
        start=newone;
        newone->next=t;
        return pos;
    }

// insert new term

    t=iptr->next;
    iptr->next=newone;
    newone->next=t;
    return pos;    
}

ostream& operator<<(ostream& s,const Poly2& p)
{
    BOOL first=TRUE;
    GF2m a;
    term2 *ptr=p.start;
    if (ptr==NULL)
    { 
        s << "0";
        return s;
    }
    while (ptr!=NULL)
    {
        a=ptr->an;
        if (!first) s << " + ";
        if (ptr->n==0) 
           s << a; 
        else 
        {
            if (a!=(GF2m)1)  s << a << "*x"; 
            else            s << "x";
            if (ptr->n!=1)  s << "^" << ptr->n;
        }
        first=FALSE;
        ptr=ptr->next;
    }
    return s;
} 


Poly2 compose(const Poly2& q,const Poly2& p)
{ // compose polynomials
    // assume P(x) = P3x^3 + P2x^2 + P1x^1 +P0
    // Calculate P(Q(x)) = P3.(Q(x))^3 + P2.(Q(x))^2 ....

    Poly2 poly;
    Poly2 temp(p);
    int qdegree;
    term2 *qptr = q.start; 
    poly.start = NULL;

    while(qptr != NULL) {
        qdegree = qptr->n;
        if(qdegree > 0) {
            temp = p;
            for(int i = 1; i < qdegree; i++)
                temp = temp * p;

            poly += temp;
        } else {
            poly = poly + qptr->an;
        }

         qptr = qptr->next;
     }

    return poly;
}